1. Field of the Invention
The present invention relates to a vane pump.
2. Description of the Related Art
As a vane pump, as described in Japanese Patent Application Laid-Open No. 2007-120435 (patent document 1), there is a structure having a housing, a rotor which is arranged in an inner portion of the housing so as to rotate, and a plurality of vanes which are slidably arranged in a plurality of vane grooves provided in a diametrical direction of the rotor. A tubular cam ring is arranged in such a manner as to surround the rotor in an inner portion of the housing. A pair of plates pinch the rotor, the vanes and a cam ring from both sides. A high pressure chamber is provided between the housing and one of the pair of plates, and is supplied a liquid discharged on the basis of a rotation of the rotor. A back pressure groove is formed in a surface coming into contact with a side surface of the rotor in one of the pair of plates, communicates with a space close to a bottom portion of the vane groove defined by a base end of the vane within the vane groove whatever rotational position of the rotor, and communicates with the high pressure chamber. A fluid supplied to the high pressure chamber is introduced to the space close to the bottom portion of the vane groove of the rotor via the back pressure groove formed in the one plate. A leading end of the vane is brought into contact with the cam surface in an inner periphery of the cam ring on the basis of the pressure of the fluid which is introduced to the space close to the bottom portion of the vane groove.
In accordance with this, in the vane pump described in the patent document 1, the leading end of the vane is pressed against the cam surface of the cam ring on the basis of a centrifugal force at the start of the rotation of the rotor. However, after a discharge pressure is generated, the discharge pressure is conducted to the back pressure groove, and the leading end of the vane which is pushed out by the discharge pressure increases a contact pressure of the cam ring with the cam surface, thereby securely achieving a trap of the pressure fluid which is pressurized between the adjacent vanes.
In the prior art, the back pressure groove formed in the one plate is formed as an annular shape of a complete round. On the other hand, a space close to the bottom portion of the vane groove which is defined by a base end of the vane within the vane groove provided in a diametrical direction of the rotor is defined by the base end of the vane and is formed in the smallest diameter side of the rotor, at the maximum pressing rotational position at which each of the vanes rotating together with the rotor is pressed into the vane groove on the basis of the contact with the cam surface of the cam ring to the maximum.
Therefore, whatever rotational position the rotor exists, a diameter of the annular ring mentioned above of the back pressure groove to be inserted into the space close to the bottom portion of the vane groove in the rotor comes to a smaller diameter than the base end position of the vane at the maximum pressing rotational position mentioned above, since the back pressure groove is formed as the annular shape of the complete round.
This means that a distance becomes smaller in all the areas in a periphery direction of the back pressure groove, the distance being formed by the back pressure groove formed in the one plate with respect to a center hole of the one plate through which a rotating shaft of the rotor passes. In other words, the distance being a seal width which prevents the discharge pressure guided to the back pressure groove from leaking to the center hole via a side clearance between the plate and the rotor. In the prior art, the discharge pressure guided to the back pressure groove formed in the one plate tends to leak to the center hole which passes through the plate.
In the case that a side clearance between the one plate and the rotor is made smaller in order to prevent the leak of the discharge pressure mentioned above, there is caused a disadvantage which deteriorates a sticking toughness of the rotor.